The invention relates to an addressing process for plasma panels based on repeating bits on one or more lines.
On plasma displays, the grey level is not produced in a conventional manner using amplitude modulation of the signal but rather temporal modulation of this signal, by exciting the corresponding pixel for a greater or lesser time depending on the level desired. It is the phenomenon of integration by the eye which makes it possible to render this grey level. This integration is performed during the frame scan time.
The eye actually integrates much faster than the frame duration and is therefore liable to perceive, in cases of particular transition of the addressing bits, variations in level which do not reflect reality. Contour defects or xe2x80x9ccontouringxe2x80x9d as it is known, may thus appear in the moving images. These defects may be compared to poor temporal restitution of the grey level. More generally, false colours appear on the contours of objects, each of the cells of a colour component possibly being subject to this phenomenon. This phenomenon is even more harmful when it occurs in relatively homogeneous zones.
The object of the invention is to overcome the aforementioned drawbacks.
To this end, the subject of the invention is a process for addressing cells arranged as a matrix array, each cell being situated at the intersection of a line and a column, the array having line inputs and column inputs for displaying grey levels defined by video words making up a digital video signal, the column inputs each receiving a control word for this column corresponding to the video word relating, for this column, to the addressed line, this word being made up of n bits transmitted sequentially, each bit triggering or not triggering, depending on its state, the selection of the cell of the addressed line and of the corresponding column for a time proportional to the weight of this bit within the word, characterized in that it consists in simultaneously selecting at least two lines for at least one of the bits of the column control word relating to one of the two lines.
According to a particular embodiment, the process is characterized in that it also carries out a transcoding of the digital video signals into column control words such that at least one of the weights of the video control words is different from a power of two, the word retaining a maximum value equal to that of the words of the video signal, in such a way that words of the video signal can correspond to different column control words, these control words then being chosen as a function of the identity of the bit or bits in respect of which at least two lines are simultaneously addressed.
The invention also relates to a device for implementing the process comprising a video processing circuit for processing the video data received, a correspondence memory for transcoding these data, a video memory for storing the transcoded data, the video memory being linked to column drivers in order to control the column addressing of the plasma panel on the basis of column control words, a control circuit for the line drivers, characterized in that the control circuit for the line drivers simultaneously selects at least two successive lines during the transmission by the column drivers of at least one of the bits of the column control words relating to one of these lines.
By virtue of this invention, the contouring defect is strongly attenuated if not eliminated. The process according to the invention is simple and inexpensive to embody and can be applied to any type of plasma panel.
According to the particular embodiment, the errors in copying from one line to another are considerably reduced and the overbrightness defect is also attenuated.